Hip prosthesis

ABSTRACT

A femoral insert combines bone ingrowth surfaces in the proximal portion of the shaft which is wide in the medial-lateral direction and curved in the medial aspect with a distal portion which has a round cross-section and is curved in the direction of the anterior bow of the femur. Accordingly, firm fixation of the implant is initially provided by the distal portion functioning as an intramedullary rod while long term stabilization is achieved proximally through bone ingrowth. Also, the neck connecting the spherical head to the shaft through the collar is anteverted with respect to the collar at an angle of about 10° to 12°. The prosthesis for the left femur is basically a mirror image of the prosthesis for the right femur.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a femur prosthetic device. More particularly,this invention relates to a hip prosthesis adapted for insertion intothe upper medullary canal in the femur of a patient. The hip prosthesisof this invention is of the type generally characterized as including ahead or ball member, a shaft member for insertion into theintermedullary canal, and a neck member connecting the ball and shaft orstem member, and also including at least one porous metal surfaceportion which provides for stabilization by bone ingrowth withoutrequiring any cement.

2. Description of the Prior Art

Hip prostheses are known in the art and these have included variousdesign configurations of the various components, including the headmember, neck, collar and shaft. Both straight and curved shafts as wellas fluted shafts are known. Representative of these known hip prosthesesare those described in the following: U.S. Pat. No. 4,279,042--T. P.Andriacchi, et al; U.S. Pat. No. 3,965,490--I. P. Murray, et al; U.K.Patent Application, G.B. No. 2,069,340A--K. Hardinge. Known commercialproducts include the Bard Contour™ and Link SP-femoral hip prosthesis,manufactured by Waldemar Link Hamburg, West Germany and the IsoelastiqueButel hip prosthesis by Butel, Grenoble, France.

Prosthetic devices provided with porous surfaces for bone ingrowth arealso known, e.g. U.S. Pat. No. 3,906,440--W. Rostoker, et al and BritishPat. Spec. No. 1,554,454--J. C. Bokros.

Nevertheless, further improvements in the total design of hip prosthesisare required to assure stable fixation of the implanted prosthesis atthe bone/metal interface. Thus, in cemented prosthetic devices there hasnot been satisfactory fixation due to the various stress loads, i.e.compression, shear and torsion, to which the implanted device issubjected. These mechanical forces, especially shear and torsion, weakenthe bone cement bond. In addition, it is known that there is a tendencyfor bone resorption which also weakens the cement bond between the bone,e.g. intramedullary canal of the femur, and the femoral prosthesis.

On the other hand, by providing a bone ingrowth surface on theprosthetic device a more stable fixation would be expected and someadvances along these lines have been made. However, experiments by thepresent inventors have shown that bone ingrowth requires the prosthesisto be stably fixed without movement for at least six weeks and anyrelative motion of the prosthesis during that period prevents orminimizes bony ingrowth.

As a result, an incidence of ten to twenty percent of femoral stemloosening or failure in total hip arthroplasty patients followed over 5or more years, especially in younger patients, has been reported.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a femoral hipprosthesis which avoids these problems of prior art devices.

A particular object of the invention is to provide a femoral hipprosthesis which combines long term stabilization by bone ingrowthproximally with initial stable fixation distally.

A further object of the invention is to provide a hip prosthesis whichclosely approximates in geometry and curvature the natural femur,including a curved long stem or shaft having a fluted design in thedistal portion, to obtain maximum torque resistance, which is wide inthe medial-lateral direction and curved medially in the proximal portionto maximize bone-prosthesis contact area, and which has a bone ingrowthmedia on both the anterior and posterior aspects in the proximal portionof the shaft.

A still further object of the invention is to provide a femoral hipprosthesis in which the femoral head and neck are anteverted from thecollar at about 10°, and at an angle with respect to the shaft of theprosthesis of about 135°, and wherein the collar extends medially fromthe prosthesis to allow load (stress) sharing and distribution with thebone to an extent of about 30% of the total load, with the remaining 70%being borne by the shaft (stem).

Generally speaking, these and other objects of the invention, which willbecome evident from the following more detailed description and specificembodiments, are accomplished by a femoral insert for hip jointprosthesis having a spherical shaped head member, a neck memberconnected to the head member and terminating at a collar, and a shaftmember connected at its proximal end to the collar and including aproximal portion and a distal portion. The proximal portion has across-section which is rectangular at the proximal end at the collar andgradually tapers to a relatively constant square cross-section. Thedistal portion of the shaft member or stem has the configuration of andfunctions as an intramedullary rod, for example, a generally circularcross-section which is curved to match the anterior bow of the femur.The upper half of the proximal portion is wide in the medial-lateraldirection with flat anterior and posterior sides, is curved medially,and may be straight or curved in the lateral aspect. The lower half ofthe proximal portion is straight in the medial and lateral aspects aswell as in the anterior and posterior sides. A porous bone ingrowthsurface, such as sintered titanium metal, is provided on at least one ofthe proximal anterior and proximal posterior sides. The collar is flushwith the anterior and posterior sides and extends medially. Accordingly,firm fixation of the prosthesis is initially provided by the distalintramedullary rod portion while long term stabilization is achievedproximally through the bony ingrowth surface.

The neck member may be anteverted with respect to the collar at an angleof about 10° to about 20° and may be at an angle to the longitudinalaxis through the proximal portion of the shaft of about 125° to about140°. The curved distal portion of the shaft is also preferably fluted.

In one embodiment, the lateral aspect of the shaft is straight in theentire proximal portion. In an alternative embodiment, the upper portionof the lateral aspect is curved over about the same or shorter length asthe medial curve but with a slightly smaller radius of curvature. Inthis embodiment, the curved upper portion of the lateral aspect includesan upstanding curved rib which extends from the underside of the collarand terminates tangentially into the body of the lateral aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with respect tospecific embodiments thereof with the aid of the accompanying drawingsin which:

FIG. 1 is a front elevation view of an embodiment of the prostheticdevice of the invention shown installed within the intramedullary of aleft femur;

FIG. 2 is a side elevation view of the left leg prosthetic device ofFIG. 1;

FIG. 3 is a top view of the left leg prosthetic device of FIG. 1;

FIG. 4 is a front elevation view similar to FIG. 1 of a right legprosthetic device according to the invention;

FIG. 5 is a side elevation view of the right leg prosthetic device ofFIG. 4;

FIG. 6 is a top view of the right leg prosthetic device of FIG. 4;

FIG. 7 is a section view in the direction of line 7--7 of FIG. 4.

FIG. 8 is a section view in the direction of line 8--8 of FIG. 4;

FIG. 9 is a section view in the direction of line 9--9 of FIG. 4;

FIG. 10 is a partial side elevation view of an alternative embodiment ofa left leg prosthetic device according to the invention.

FIG. 11 is a view, partially in section, in the direction of line 11--11of FIG. 10; and

FIG. 12 is a section view in the direction of line 12--12 of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

Firm implantation of the femoral insert prosthetic device of thisinvention is provided by combining a unique configuration of thecomponent parts, namely spherical head, neck, collar, and shaft whichclosely approximate the natural configuration of the normal femoralshaft, femoral neck and head, and specifically an anteverted femoralneck, with a shaft which, in the proximal portion, is wide in themedial-lateral direction, at least partially straight in the lateraldirection and curved in the medial direction to match the inside contourof the femoral shaft and in the distal portion is fabricated to theconfiguration of an intramedullary rod, preferably it is curved to matchthe anterior bow of the femur. Opposite curvatures are provided for eachof the left and right leg femoral prostheses.

In addition, at least one of, and preferably both, the anterior andposterior aspects are provided with a bone ingrowth surface and,therefore, the need for cement fixation, which is one of the majorcauses of total hip failure, is eliminated.

Accordingly, firm fixation is achieved in the greater trochanter regionby making the upper segment (proximal end) of the shaft broad in themedial-lateral direction. The bone ingrowth surfaces on the anteriorand/or posterior aspects provide still further fixation of the proximalportion of the shaft while the intramedullary rod portion of the shaftat the distal end is firmly fixed by virtue of its being curved tostimulate the anatomical configuration of the normal femur. The initialstable fixation of the distal intramedullary rod portion of the shaft inthe intramedullar of the femoral shaft permits bone ingrowth to occurproximally to provide an overall secure fit of the entire prosthesiswithout requiring any adhesive cement.

Turning now to to the drawings, a left femoral prosthesis is showngenerally at 1 in FIGS. 1-3. The prosthetic device includes sphericalhead member 2, neck member 3, collar 4 and shaft member 5. Theprosthetic device is preferably fabricated from titanium metal ortitanium alloy, but any other biologically compatible, inert metal thathas sufficient mechanical strength can be used.

FIGS. 4, 5 and 6 are similar to FIGS. 1, 2 and 3, respectively, but arefor a right femoral prosthesis. In FIGS. 4-9, the spherical head member,neck member, collar and shaft member are designated by 42, 43, 44 and45, respectively.

As will be described in greater detail below, the direction ofangulation of the neck member and the direction of the curved bow of thedistal stem portion are in one direction for the left femoral prosthesisand in the opposite direction for the right femoral prosthesis. However,the right and left femoral prostheses are otherwise constructed in thesame manner and are, generally speaking, mirror images of each other.

Head member 2, 42 is generally globular in shape and assumes somewhatmore than a hemisphere. The head member has a highly polished bearingsurface to mate with the hip socket, which may be the natural hip socketor an artifical prosthesis in the case of total hip replacement. Thefemoral head member has a diameter of about 28 millimeters, althoughsmaller and larger sizes can be stocked or prepared as needed forindividual patients.

The underside 52 of head member 42 is substantially flat (FIG. 7),although it can also be slightly curved, either convexly or concavely,to where the neck member joins the underside in substantially the centerportion thereof.

The neck member which connects the head member to the shaft at thecollar, is generally rectangular in cross-section and is broader in theinferior and superior direction than in the anterior and posteriordirection. The base of the neck at the collar is broader than its apexwhere it joins the head to approximate the pyrimidal configuration of anormal femoral neck. Additional structural strength is provided byhaving the base and the apex diverge outwardly at the juncture with thecollar and head member, respectively.

As best seen in FIG. 2, the longitudinal axis 13 of neck 3, intersectsthe longitudinal axis 15, of shaft 5 at an angle α in the range of 125°to 140°, preferably about 135°. The neck member is also anteverted withrespect to the collar by the angle β, between longitudinal axis 13 andline 14 which is an extension of longitudinal axis 15 of shaft member 5through the upper proximal portion thereof, which ranges from about 10°to about 20°, preferably about 10° to 12°, especially about 10°. As seenin FIG. 3, line 14 is parallel to and equidistant from the anterior andposterior edges of collar 4.

Collar 4, 44, extends medially from the shaft member at extension 16, 56but is otherwise flush with the lateral sides of the shaft member. Asseen in FIG. 7, extension 56 has an arcuate elliptical periphery 59which bulges slightly from either of the anterior 57 and posterior 48lateral sides of shaft member 45. The extended collar rests on the uppersurface of the femoral shaft bone (as shown in phantom outline in FIG. 1and FIG. 2) to provide for medial load transfer and stabilization of theimplanted prosthesis.

The upper proximal portion 6 of shaft member 5 is broad in themedial-lateral direction with the greatest width occurring at thejuncture with collar 4 and gradually tapering to a substantiallyconstant width at or near the midpoint thereof. In the widened uppermedial-lateral region of the upper proximal portion bone ingrowth pads20 and 60, 61 are provided on the anterior and posterior lateral sides,respectively. These are preferably formed from sintered titanium metalof 300-400 microns pore size, although any other bone ingrowth media orconstruction can be used. Preferably, as shown in FIG. 7, the boneingrowth pads are securely fitted within the notched undercut portions62, 63 in the anterior and posterior lateral faces 57, 58, respectively.The outer surfaces of the bone ingrowth pads are preferably flush withthe lateral sides 17, 18 and 57, 58, respectively. The configuration ofthe bone ingrowth pads is not particularly critical but generally theywill be in the same general configuration as the lateral sides andshould cover the majority of the surface area of the upper portion, forexample, about 50 to about 90%, of the area of the upper portion, orabout 1 to 3 square inches for each pad.

The upper proximal portion has a straight lateral aspect 26 and isslightly curved in the upper half of the medial aspect 24 to match theinside contour of the femoral shaft thereby allowing for firm fixationin the greater trochanteric region. The curve of the upper medial aspectmakes a smooth transition with the lower flat medial aspect which issubstantially parallel to the straight lateral aspect.

The lower distal portion 7 of shaft member 5 is curved to match theanterior bow of the femur and is fluted over its entire length which isabout one-half of the total length of the shaft member from collar 4 tothe free end 31. The curved/fluted configuration enables the distalportion to function as an intramedullary rod to again provide firmfixation of the prosthesis in the femoral shaft at the distal end sothat bone ingrowth can proceed at the proximal end.

As can be seen from FIGS. 1 and 4, the curve of the distal portion ofthe shaft is in the opposite direction than the direction of anteversionof neck member 3, 43. This can also be seen in FIGS. 3 and 6 where thefree end 31, 71 of the shaft member is "behind" collar 4, 44 or into theplane of the paper while neck member 3, 43 and head member 2, 42 are "infront of" collar 4, 44 or out of the plane of the paper. In other words,the right hip prosthesis and left hip prosthesis are mirror images ofeach other.

As seen in FIG. 8, the lower half of the upper proximal portion 46 ofshaft member 45 has a substantially square cross-section with slightlyrounded corners. The upper half of the upper proximal portion whichincludes the curved medial aspect 64 has a rectangular cross-section(FIG. 7). The fluted distal portion 47 has a substantially circularcruciform cross-section (FIG. 9). Flutes 8, 48 are cicumferentiallyspaced at 90° intervals around the distal portion 7, 47 and their edgesmerge smoothly into the rounded ribs 9, 49 which separate them and whichare circumscribed within a circle having a diameter which issubstantially equal to the length of a side of the square cross-sectionof the upper proximal portion 6, 46, i.e. the distance between themedial and lateral aspects and between the anterior and posterior sides.The width and depth of each of the four flutes is substantially constantalong the length of the distal portion.

FIGS. 10, 11 and 12 illustrate a slightly modified embodiment of a hipprosthesis (illustrated for the left hip only) according to theinvention.

In this embodiment, the lateral aspect 126 in the upper region 135 ofthe upper proximal portion 106 is also curved but with a somewhatsmaller radius of curvature than the radius of curvature for the curvedmedial aspect 124. Curved rib 138 is provided in the central portion ofthe upper region 135 beginning at the underside of collar 104 andterminating in the lateral aspect at or near the transition from thecurved upper region 135 to the straight lower region 136 of lateralaspect 126. As seen in FIGS. 10 and 11, rib 138 blends smoothly andtangentially into the lateral aspect. By appropriate reaming of thegreater trochanteric region of the femur additional contact area can beprovided between the prosthesis and the femur at the rib 138. Also inthis embodiment the extension 116 on collar 104 has a more roundedconfiguration than the elliptical configuration of extension 16 and doesnot bulge beyond the lateral walls.

It is envisioned that the hip prosthesis can be stocked in severalstandard sizes and combinations. For example, the femoral neck can bestocked in lengths 1 of 28 mm, 30 mm, 34 mm and 40 mm, measured from thebase of the collar to the center of the femoral head. Standard sizes forthe length L of the shaft member, measured from the base of the collarto the free end, would typically be 200 mm, 220 mm, 230 mm, 250 mm, 260mm and 270 mm.

For a typical embodiment of the right and left femoral insertsillustrated in FIGS. 1-9 with a 28 mm diameter spherical head the neckmember will be about 34 mm in length, the overall length of the collarLC will be about 42 mm, the width W is about 15 mm, the length L isabout 230 mm and the length of the fluted distal portion is about 125mm.

Accordingly, the hip prosthesis of the present invention will have thefollowing advantages:

1. Allows early weight bearing, such as in conventional total hiparthoplasty, but not present ingrowth systems;

2. Avoids use of cement;

3. Ideal for young patients, need not enlarge acetabulum in contrast toresurfacing arthoplasty;

4. Does not require any unconventional surgical procedures sinceorthopaedic surgeons are familiar with reaming the intramedullary canal;

5. Reduces loosening by a combination of proximal bony ingrowth anddistal fixation.

What is claimed is:
 1. In a femoral insert for hip joint prosthesishaving a spherical shaped head member, a neck member connected to thehead member and terminating at a collar, and a shaft member having aproximal portion connected to the collar and extending approximatelyhalf the extent of the shaft member, and a distal portion extendingtherefrom, the improvement comprisingthe collar being flush to theanterior and posterior sides of and extending medially from the shaftmember; the proximal portion having a longitudinal axis and asubstantially straight lateral aspect, an upper half which is broad inthe medial-lateral direction and curved in the medial aspect and havinga generally rectangular cross-section which is widest at the collar andgradually tapers to a generally square cross-section, and a lower halfwhich has flat sides and a generally square cross-section of the upperhalf; said neck member being anteverted with respect to the collar andproximal portion at an angle of about 10° to 20° and is at angle to saidlongitudinal axis through said proximal portion of said shaft member ofabout 125° to about 140°; at least one of the anterior and posteriorsides of the upper half of said proximal portion including at least oneporous bony ingrowth surface; and said distal portion having the curvedconfiguration of an intramedullary rod and curving in the oppositedirection from the direction of said anteversion of said neck member,and said proximal portion extending straight in a plane parallel to saidlateral aspect, whereby firm fixation of the prosthesis is initiallyprovided by the distal intramedullary rod portion while long termstabilization is achieved proximally through the bony ingrowth surface.2. The femoral insert of claim 1 wherein the distal portion has agenerally circular cross-section.
 3. The femoral insert of claim 1 or 2wherein the distal portion is curved to match the anterior bow of thefemur.
 4. The femoral insert of claim 3 wherein the distal portion isfluted.
 5. The femoral insert of claim 1 or 2 wherein the distal portionis fluted.
 6. The femoral insert of claim 1 wherein the angle β is about10° and the angle α is about 135°.
 7. The femoral insert of claim 1wherein said straight lateral aspect extends in both the upper and lowerhalves of the proximal portion.
 8. The femoral insert of claim 1 whereinthe medial aspect is curved in the upper half of the proximal portionand is flat in the lower half of the proximal portion.
 9. The femoralinsert of claim 5 in which the upper half of the lateral aspect furthercomprises an upstanding curved rib which extends from the underside ofthe collar and terminates tangentially into the body of the lateralaspect.
 10. The femoral insert of claim 1 which comprises porous boneingrowth surfaces on both the posterior and lateral sides comprising acoating of a sintered titanium metal or alloy having a pore size in therange of 300 to 400 microns.
 11. A femoral insert for hip jointprosthesis which comprises a spherical shaped head member, a neck memberconnected to the head member and terminating at a collar, a long stemmember having a proximal portion connected to the collar and extendingapproximately half the extent of the shaft member, and a distal portionextending therefrom and having the curved configuration of anintramedullary rod and being curved to match the anterior bow of thefemur, the proximal portion of said long stem having an upper half whichis broad in the medial-lateral direction and curved in the medial aspectto match the inside contour of the femoral shaft and having a generallyrectangular cross-section which is widest at the collar and graduallytapers to a generally square cross-section, said proximal portion havinga longitudinal axis being straight in the anterior and posterioraspects, and a lower half which has flat sides and substantially thesame generally square cross-section as that of the upper half, said neckmember being anteverted with respect to the collar and proximal portionat an angle β of about 10° to 20°, said distal portion of said stemmember being curved in a direction opposite to the direction of saidanteversion of said neck member, said long stem member having a lengthof at least about 200 mm and sufficient to extend to the intramedullarycanal, said neck member forming an angle to said longitudinal axisthrough the proximal portion of the stem member of about 125° to about140°, and porous bone ingrowth surfaces on both the posterior andlateral sides of the upper half of the proximal portion of the stemmember,whereby firm fixation of the prosthesis is initially provideddistally by the long curved stem and proximally by the broad upper halfof the proximal portion of the stem member fitting tightly in the reamedout portion of the femoral canal, including bone-prosthesis contact areaat the curved medial aspect and long term stabilization is achievedproximally through the growth of bone into the bony ingrowth surfaces.12. The femoral insert of claim 11 wherein the distal portion has agenerally circular cross-section and is fluted, and said porous boneingrowth surfaces comprise a coating of a sintered titanium metal oralloy having a pore size in the range of 300 to 400 microns. .Iadd. 13.In a femoral insert for hip joint prosthesis having a spherical shapedhead member, a neck member connected to the head member and terminatingat a shaft member having a proximal portion connected to the neck memberand extending approximately half the extent of the shaft member, and adistal portion extending therefrom, the improvement comprising:theproximal portion having a longitudinal axis and a substantially straightaspect, an upper half which is broad in the medial-lateral direction andcurved in the medial aspect and having a generally rectangularcross-section which is widest adjacent the neck member and graduallytapers to a generally square cross-section, and a lower half which hasflat sides and a generally square cross-section of the upper half; saidneck member being anteverted with respect to the proximal portion at anangle of about 10° to 20° and is at an angle to said longitudinal axisthrough said proximal portion of said shaft member of about 125° toabout 140°; at least one of the anterior and posterior sides of theupper half of said proximal portion including at least one porous bonyingrowth surface; and said distal portion having the curvedconfiguration of an intramedullary rod and curving in the oppositedirection from the direction of said anteversion of said neck member,and said proximal portion extending straight in a plane parallel to saidlateral aspect, whereby firm fixation of the prosthesis is initiallyprovided by the distal intramedullary rod portion while long termstabilization is achieved proximally through the bony ingrowthsurface..Iaddend. .Iadd.
 14. A femoral insert for hip joint prosthesiswhich comprises a spherical shaped head member, a neck member connectedto the head member and terminating at a long stem member having aproximal portion connected to the neck member and extendingapproximately half the extent of the shaft member, and a distal portionextending therefrom and having the curved configuration of anintramedullary rod and being curved to match the interior bow of thefemur, the proximal portion of said long stem having an upper half whichis broad in the medial-lateral direction and curved in the medial aspectto match the inside contour of the femoral shaft and having a generallyrectangular cross-section which is widest at the neck member andgradually tapers to a generally square cross-section, said proximalportion having a longitudinal axis being straight in the interior andposterior aspects, and a lower half which has flat sides andsubstantially the same generally square cross-section as that of theupper half, said neck member being anteverted with respect to theproximal portion at an angle β of about 10° to 20°, said distal portionof said stem member being curved in a direction opposite to thedirection of said anteversion of said neck member, said long stem memberhaving a length of at least about 200 mm and sufficient to extend to theintramedullary canal, said neck member forming an angle to saidlongitudinal axis through the proximal portion of the stem member ofabout 125° to about 140°, and porous bone ingrowth surfaces on both theposterior and lateral sides of the upper half of the proximal portion ofthe stem member,whereby firm fixation of the prosthesis is initiallyprovided distally by the long curved stem and proximally by the broadupper half of the proximal portion of the stem member fitting tightly inthe reamed out portion of the femoral canal, including bone-prosthesiscontact area at the curved medial aspect and long term stabilization isachieved proximally through the growth of bone into the bony ingrowthsurfaces..Iaddend.